San Francisco Mayor Ed Lee issued a challenge to the crowd attending the Web 2.0 Summit at the Palace Hotel today: Build a smart phone app that will warn people if their car is about to be towed or if they parked in a tow-away zone.

Lee noted that in two years, the city is hosting the America’s Cup yacht race, an event that could bring about 500,000 visitors into the city on any given day. That’s also going to bring a flood of people looking for already scarce parking space, and they could benefit from that tow-warning app.

“We can save a lot of people from having disappointment in their lives,” said Lee, who is in a heated race to see if he’ll even be mayor in 2013.

Such an app could also cost the city some parking fine revenues, but Lee was playing to an audience of tech executives who could bring a lot more to the city’s economy.

Lee said there were now 1,500 technology companies with 27,000 employees in San Francisco. And there were 40 tech companies looking to lease about 2 million square feet of office space in the city, the equivalent of about four Transamerica Pyramids, he said.

Before his short welcome speech, Lee spent time working the crowd and learning about data, with noted angel investor Ron Cowan making the introductions.

UPDATE:

Readers have noted that Lee’s mayoral rival, Board of Supervisor’s President David Chiu, called for legislation last month requiring the city’s transportation and public works agencies to create a towing notification service, including the development of smart phone apps.

After Lee’s speech this morning, his communications director, Christine Falvey, sent over this e-mail:

“The mayor would like to work with both President of the Board David Chiu and City Assessor Phil Ting on the idea of a tow truck app. Both the Board President and the assessor have come up with some good ideas on this and the mayor would like to make sure they are successful.”

Perhaps the app developers here at Web 2.0 should also come up with a political brouhaha warning app.